Brain Uses Loudness Of Vowels To Process Speech Into Syllables : Shots - Health News Syllables are the building blocks of spoken language. And now a study of brain activity hints at how we extract them from a stream of speech.
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The Loudness Of Vowels Helps The Brain Break Down Speech Into Syl-La-Bles

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The Loudness Of Vowels Helps The Brain Break Down Speech Into Syl-La-Bles

The Loudness Of Vowels Helps The Brain Break Down Speech Into Syl-La-Bles

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ARI SHAPIRO, HOST:

As you listen to this sentence, your brain is breaking down a stream of words into syllables. That process is critical to understanding speech. And now scientists think they know how it works. NPR's Jon Hamilton has more.

JON HAMILTON, BYLINE: A familiar sonnet by Shakespeare...

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UNIDENTIFIED PERSON: Shall I compare thee to a summer's day?

HAMILTON: ...One line, 10 syllables. And our brains detect each one of those syllables. But how? That's what Yulia Oganian and a colleague at the University of California, San Francisco wanted to know. So they looked at a part of the brain called the superior temporal gyrus.

YULIA OGANIAN: That's an area that has been known for over 150 almost years to be really important for speech comprehension. So we knew if we can find syllables somewhere, it should be there.

HAMILTON: The team studied a dozen patients preparing for brain surgery. Oganian says that meant they already had electrodes in place monitoring the brain area involved in speech.

OGANIAN: So then we asked our patients to lay back and relax and listen.

HAMILTON: They heard lots of sentences, including that bit of Shakespeare.

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UNIDENTIFIED PERSON: Shall I compare thee to a summer's day?

HAMILTON: And their brain activity suggested that changes in volume were the key to detecting syllables. But it all happened so fast that there was no way to tell exactly when the brain was responding. So they had a computer slow down each sentence.

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UNIDENTIFIED PERSON: Shall I compare thee to a summer's day?

HAMILTON: Oganian says that revealed the precise timing.

OGANIAN: What we saw with the slow speech is that the neural response went up every time the speech intensity started to rise fast.

HAMILTON: The brain was using an abrupt increase in volume as a marker for each syllable. And that increase, at least in English, was occurring at the beginning of each vowel sound. Oganian says the team also noticed something else. The brain could tell whether a vowel was stressed or unstressed.

OGANIAN: So, for example, in summers, there's suh-mmers (ph).

HAMILTON: The uh (ph) sound in summer gets stressed while the er (ph) sound gets less emphasis. Oganian says detecting this difference is critical because stressed and unstressed syllables help create the rhythm of human speech. The idea that the brain might use just one type of volume change to detect syllables has been debated for many years. But Oded Ghitza of Boston University says the system suggested by Oganian's team makes sense.

ODED GHITZA: It is in line with the model that we propose.

HAMILTON: The model Ghitza is talking about is a computer model meant to simulate the way a human brain decodes speech. And Ghitza says detecting syllables is critical.

GHITZA: We are talking one to another until there's a stream going on, right? So how the brain deals with the stream?

HAMILTON: Ghitza says one way is to break the stream into separate parts called syllables.

GHITZA: That's the basic Lego block of language.

HAMILTON: Including poetry. The new research appears in the journal Science Advances. Jon Hamilton, NPR News.

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